**Distributed Sources**
This applet modeling is based on a first-order,
at steady state, linear differential equation with constant parameters (flow, area, depth) over a given length:

where:
*S* = Substance Concentration at x = x(t) (mg/L)

*S*_{D} = Substance Distributed Concentration (mg//L)

*K* = Decay Constant (1/day)

*t *= Travel Time (day) = x / U

U = Stream Velocity (mi/day; mpd)

L = Distributed Source Length (mi)